Epoxy resins based on macrocyclic compounds

ABSTRACT

Macrocyclic epoxy resins comprising at least one compound of the formula (I) ##STR1## wherein n is an integer from 3 to 10. 
     R 1  and R 3  are either the same or different and are selected from hydrogen, hydroxyl, alkoxy, allyloxy and epoxypropyloxy (glycidyloxy); 
     R 2  is selected from hydrogen, arylakalkyl optionally substituted with halogen, alkyl optionally substituted with halogen, and aryl optionally substituted with halogen; 
     R 4  is selected from hydrogen, alkyl optionally substituted with halogen, arylalkyl optionally substituted with alkyl or halogen, and aryl optionally substituted with halogen; 
     R 5  is selected from hydrogen, aryl and alkyl; with the proviso that the resin contains on average at least one epoxy group per molecule.

The invention relates to epoxy group-containing macrocyclic compoundssuitable for use as epoxy resins which when formulated and cured givepolymer matrices having high glass transition temperatures.

In this specification the term "epoxy resin" is used to denote a mixtureof chemical compounds containing on average one or more epoxy groups permolecule. Epoxy resins are commonly reacted with curing agents(hardeners) usually in the presence of other additives such ascatalysts, toughening agents, reinforcing fibres or fillers, to producecrosslinked cured resin composites which are useful for structuralpurposes. Such mixtures of ingredients before reaction occurs arereferred to as curable epoxy resin formulations; all ingredients may becombined in one container (one-pack formulation) or the epoxy resin andcuring agents may be in separate containers (two pack formulation). Inthe latter case the two parts Of the formulation are mixed immediatelybefore curing.

Epoxy resins based on phenols form a significant portion of thethermosetting resins in commercial use. Of these epoxy resins, thediglycidyl ethers of bisphenol A (DGEBA) and their analogues are themost important for use in composite materials and adhesives. Other epoxyresins based on phenol/formaldehyde Novolac resins are also used andoffer advantages in some applications. Existing resins of this lattertype are glycidyl derivatives of linear oligomers made from variousphenols and formaldehyde.

The glycidyl ether type epoxy resins known in the art, when cured, tendto have glass transition temperatures (T_(g)) which are too low for hightemperature use, for example, as matrices in composite materials for usein advanced aerospace and automotive applications. A low T_(g) of thematrix material leads to an early fall-off in mechanical properties of alaminate with rise in temperature.

Epoxy resins of a different type in which the glycidyl ether groups arereplaced by N-glycidyl substituents have been developed which showlimited improvement in T_(g). These are used extensively in the advancedcomposites industry at the present time. However, they have thedisadvantage of being based on highly toxic bisarylamines such asmethylene dianiline and have different cure characteristics to theglycidyl ether-type resins which can lead to a problem of differentialcuring and deterioriation in mechanical properties in compositionscontaining both types.

The present invention provides an alternative to this latter approachwhich uses glycidyl ether-type epoxy resins based on more rigidmacrocyclic structures built up from simple, cheap phenols of lowtoxicity. The cured resin formulations have better high temperatureperformance than those based on existing glycidyl ethers. Moreover, theformulations can also contain the diglycidyl bisphenol A type resinswithout significant detriment to T_(g).

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, reference will be made to the accompanying drawings,in which:

FIG. 1 is a diagrammatic representation of a calixarene; and

FIG. 2 is a plan view of an upper rim epoxy calixarene.

Macrocyclic structures can be synthesized by reaction of specificphenols with aldehydes under special conditions. These are well definedchemical compounds with Zinke and Zeigler, 1944, Ber., 77, 264; Niederland Vogel. 1940, J. Am. Chem. Soc, 62, 2512, Cornforth et al., 1955, Br.J. Pharmacol., 10, 73 making early contributions to their synthesis andstructural elucidation. More recently, Gutsche (Gutsche andMuthukrishnan, 1978, J. Org. Chem., 43,4905) has assigned such compoundsthe collective name "Calixarenes" because they often adopt aconformation in which the aryl rings are arranged to form the sides ofan urn or calix as shown in FIG. 1. It is compounds of this type thatform the precursors of the resins of the present invention.

So far, calixarenes have found only limited use in polymer chemistry. Arecent summary of such applications can be found in the article byPerrin and Harris (Topics in Inclusion Science, Vicens. J. and Bohmer,V., Eds., pp 235-257).

Gutsche et at., 1985, J. Org. Chem., 50,5802 refer to an epoxyderivative of a calixarene which was prepared fromtetra-allyl-tetra-p-tolylsulphonylcalix[4]arene during attempts toconvert this compound to the aldehyde. Oxidation with m-chloroperbenzoicacid was said to have "proceeded smoothly to yield a crystalline solid,which possesses a ¹ H nmr spectrum commensurate with epoxide structure".The product of this reaction was implied to be a5,11,17,23-substituted-(2,3-epoxy)propyl derivative of calix[4]arene.The authors later revealed that the product was a mixture and that"attempts to convert the epoxide to an aldehyde with BF₃ -etherateyielded a white, cellulose-like material that was insoluble in all theusual organic solvents".

Calixarenes can be made with hydroxy substituents in either the "lowerrim" or the "upper rim" (as shown in FIGS. 1 and 2). In U.S. Pat. No.4,259,464, which related to improved synthesis of calixarenes of thetype having the hydroxy groups on the lower rim, Buriks, Fauke and Munchsuggest that these compounds can be reacted with various reagents suchas: "Alkylene oxides, such as ethylene, propylene, butylene, styrene,etc., oxides, epihalohydrin, glycide, glycidyl ethers, epoxidized vinylcompounds, such as a-olefin epoxides etc." We have found experimentallythat the lower rim hydroxy, calixarenes of the type listed in U.S. Pat.No. 4,259,464 give only the halohydrin with epihalohydrin and will notgive an epoxy compound under the normal conditions of epoxidation.

More recently Goerman, Koecke, Bieroegel, Tarnow, Sierk and Raddatz ((DD278139 A1 (Chem. Abs. 114, (15), 142900z, 2-5-91)) have disclosed aprocess for preparing epoxy derivatives of some calixarenes. In thisprocess, glycidyl ethers are prepared by direct reaction withepichlorohydrin on calixarenes of the type described herein as "lowerrim" calixarenes and which we have found do not give epoxy derivativesnormally by direct reaction with epihalohydrins. The epoxy resins of thepresent invention are upper rim calixarenes. The novelty in DD 278139 A1resides in the use of a phase transfer agent and prolonged reactiontimes to affect the reaction. By this process, calixarenes are said tobe functionalized with groups of high reactivity for the purpose ofattaching the calixarenes to polymer or biochemical materials. There isno mention of the use of these materials as resin matrix materials. Theepoxy equivalent weights attained for the materials of DD 278139 A1 aretoo high, for example 490 g for the epoxy derivative of t-butylcalix[8]arene, to be suitable for use in composites. Furthermore, we have foundthat under curing conditions the epoxy derivatives of t-butylsubstituted calixarenes, especially in the presence of the borontrifluoride catalysts are prone to some dealkylation leading to voidagein the resultant matrix.

We have repeated the preparation described in Example 3 of DD 278139 A1and produced epoxy derivatized t-butylcalix[8]arene of epoxy equivalentweight 390 g. Curing of this material (Resin A) in our standard systemproduced an heterogeneous material of T_(g) (Tan δ 199° C.) inferior tothe resins produced in accordance with the present invention. Thisresult is similar to that obtained on curing of an epoxy derivative oft-burylcalix[8]arene synthesized by an indirect method in the presentwork and described below as Resin B.

The use of some calixarenes as hardeners with commercial epoxy resinswas described in Maeda and Uchida,1990, Netsu Kokasei Jushi, 11, 79 andin JP 02,123,126. The advantages claimed are "thermostability, greaterelasticity and a higher glass-transition temperature" in the curedresins. JP 02,123,126 states that the epoxy groups of bisphenol A typeresin did not react with the hydroxyl groups of t-butylcalix[4] and[8]arene in the presence of a primary amine such astriethylenetetramine, but did react in the presence of a tertiary aminesuch as N,N-dimethylbenzylamine.

We have now found that improved epoxy resins can be prepared from "upperrim" calixarenes such asC-methylcalix[4,]resorcinarene(2,8,14,20-tetramethyl-4,6,10,12,16,18,22,24-octahydroxycalix-4-arene)which are synthesized from reaction of resorcinol or derivatives thereofand other phenols with various carbonyl compounds. We have found thatthe use of calixarenes gives better viscosity properties to the resinsand that the resins when cured have considerably higher glass transitiontemperatures than the glycidyl ether type resins in current use.

According to one aspect of the invention there is provided a macrocyclicepoxy resin comprising at least one compound of the formula (I) ##STR2##wherein n is an integer from 3 to 10;

R¹ and R³ are either the same or different and are selected fromhydrogen, hydroxyl, alkoxy, allyloxy and epoxypropyloxy (glycidyloxy);

R² is selected from hydrogen, alkyl optionally substituted with halogen,aralkyl optionally substituted with halogen, and aryl optionallysubstituted with halogen;

R⁴ is selected from hydrogen, alkyl optionally substituted with halogen,aralkyl optionally substituted with halogen, and aryl optionallysubstituted with alkyl and/or halogen;

R⁵ is selected from hydrogen, aryl and alkyl; with the proviso that theresin contains on average at least one epoxy group per molecule.

All alkyl moieties may be straight chain or branched. Preferably suchalkyl groups contain from 1 to 20 carbon atoms.

In this specification "aralkyl" means a straight chained or branchedalkyl group. substituted with one or more aryl groups, for example,benzyl, diphenyl methyl.

Substituents R¹, R², and R³ are on the "upper rim", R⁵ is on the "lowerrim" and R⁴ is the substituent on the "bridging group" --C(R)-- of thecalixarene (see FIGS. 1 and 2).

A preferred group of compounds of the formula (I) are those wherein eachof R¹ and R³ is hydroxyl, alkoxy or epoxypropyloxy, R² is hydrogen, R⁴is methyl, ethyl or propyl and R⁵ is hydrogen.

A particularly preferred group of compounds of formula (I) are those inwhich the number of hydroxyl (or hydroxyl+alkoxy) groups isapproximately equal to the number of epoxypropyloxy groups.

Epoxy resins of this invention may be prepared either directly orindirectly by epoxidation of calixarene precursors which themselves areprepared by reaction of the appropriate phenol with an aldehyde eitherin the presence of acid or alkali under conditions which are adjusted togive cyclic structures. The methods used for the preparation of thecalixarene precursors are similar to those already described in theliterature and involve addition of the aldehyde to the phenol undercontrolled conditions in the presence of acid or base and heating in anappropriate solvent often with provision for removal of the water ofreaction. The precursors used in the present invention are those withhydroxyl groups on the "upper rim" and can be epoxidized directly withepichlorohydrin. The alternative procedure for epoxidation whichinvolves preparing the allyl ethers could be used but these derivativesundergo rapid polymerization on treatment with peracids for theoxidation. However, it will be appreciated that other suitable knownmethods could be employed.

The epoxy group content and physical characteristics of the resin can beregulated by masking the hydroxy functionality prior to epoxidation byformation of ether groups such as methoxy or alkoxy or by altering theepoxidation conditions. Chemical variations are possible on the bridgesof the resin, on the rim functionality and on the degree ofpolymerization thus allowing fine tuning of the properties.

According to another aspect of the present invention there is provided amethod for the preparation of a macrocyclic compound of the formula (I)as defined above, characterized in that said method comprisesepoxidizing a compound of the formula ##STR3## wherein n, R², R⁵ and R⁴are as defined for the compound of formula (I) and R⁶ and R⁷ are eitherthe same or different and are selected from hydrogen or a masking group,with the proviso that at least one of R⁶ and R⁷ is hydrogen.

Epoxidation may be performed using epichlorohydrin or any other suitablereagent.

According to a further aspect of the present invention there is providedan epoxy resin formulation, characterized in that the formulationcomprises an epoxy resin consisting of macrocyclic compounds of theformula (I) as defined above.

According to a still further aspect of the present invention there isprovided a curable epoxy resin formulation, characterized in that theresin comprises an epoxy resin as defined above, together with one ormore other epoxy resins and/or additives such as are known per se in theart, e.g. toughening polymers,: hardeners and catalysts.

The epoxy resins prepared generally have epoxy equivalent weightsranging from 170 to 400 and are low melting point solids. In a curableformulation they may be used as the sole epoxy resin or in admixturewith another epoxy resin, such as, for example, commercial DGEBA whichhas the advantage of being a glycidyl ether also. They may be used incombination with an amine hardener. such as, for example, the amine DDSand cured at temperatures up to 250° C. Other hardeners such asanhydrides may also be used. The curing reaction may be catalysed byaddition of, for example, BF₃ -ethylamine, BF₃ -benzylamine or otherknown catalysts. The toughening polymers may be either elastomers orthermoplastics.

The curing may be carried out using any suitable known technique suchas, for example, in an autoclave, hot platten press or other device.

Compounds of the formula (I) as stated above wherein R⁵ is hydroxyl,allyloxy or epoxypropyloxy group are discussed hereinafter for purposesof comparison. Particularly preferred epoxy resins are listed in Table 1below.

                  TABLE 1                                                         ______________________________________                                        Structures of some resins according to this invention                         Resin of                                                                      Example Number                                                                           R.sup.1 R.sup.2 R.sup.3                                                                            R.sup.4                                                                             R.sup.5                                                                             n                                 ______________________________________                                        1.         OGly    H       OH   Me    H     4                                 2.         OGly    H       OH   Et    H     4                                 3.         OGly    H       OH   i-Pr  H     4                                 4.         OGly    H       OH   Ph    H     4                                 5.         OGly    H       OMe  Me    H     4                                 6.         OGly    H       OH   n-Pr  H     4                                 7.         OGly    Me      OH   Me    H     4                                 8.         OGly    H       OH   Me    H     4                                 For Comparison Purposes                                                       Resin A    H       t-Bu    H    H     OGly, 8                                                                       OH                                      Resin B    H       t-Bu    H    H     OGly, 8                                                                       Allyl                                   ______________________________________                                         Where OGly = OCH.sub.2 CH(O)CH.sub.2                                          Notes: These are "idealized" structures. In a given resin preparation         there is a number of regioisomers present involving interchange in            position of groups at R.sup.1 and R.sup.3. Also some masking of hydroxyl      groups, giving rise to alkoxy groups, may occur during epoxidation.      

By way of example, resin formulations according to the presentinvention, which also contain the resin DGEBA, a diarylamine hardenerand a catalyst when cured by heating in stages to 180° C. with orwithout post-cure (heating unrestrained in air) have glass transitiontemperatures above 200° C. and usually in the range 270°-300° C. asshown in Table 3 (below). T_(g) values in this latter range arepreferred for the applications envisaged for the resins of theinvention. For comparison, glycidyl ether type epoxy resins of the priorart have T_(g) values up to 240° C.

Fracture toughness values (K_(q)) of the cured resin formulationscontaining only epoxy resins and hardeners are in the range 0.4 to 0.6MPa. m^(1/2). Greater toughness can be obtained by formulation of theresins with a variety of toughening agents such as various rubbers andthermoplastic materials; such formulations typically give toughnessvalues from 0.5 to 0.8 MPa.m1/2.

The epoxy resins of the present invention are particularly useful in themanufacture of fibre-reinforced composite materials.

For example, the resin formulations of the invention may be applied toreinforcing cloth such as uni-directional or woven carbon fibre eitherfrom solution (preferably a lower aliphatic ketone or halogenatedhydrocarbon solvent) or from a hot melt. Application may be manual or bya machine process including those involving transfer from a precoatedtransfer medium.

In another aspect, the present invention provides an impregnated fibrereinforced material (commonly known as a "prepreg"), characterized inthat the fibre reinforcements are impregnated with an epoxy resinformulation defined above.

The impregnated fibre materials can be laid down by any suitable knownmethod for making composite materials such as, for example, vacuumbagging on a caul plate or on an appropriate tool.

The impregnated fibre reinforced materials are suitable for use in theproduction of advanced composite materials.

Thus, in a further aspect, the present invention provides an advancedcomposite material comprising a fibrous material in a matrix of a curedepoxy resin formulation in accordance with the invention defined above.

Alternatively, the resins of the invention can be used in an appropriateformulation for resin transfer moulding or for manufacture of sheetmoulded material. Another envisaged application is in pultrusion.

The invention is further described by the following non-limitingexamples.

COMPARATIVE EXAMPLES

The preparation of a "lower rim" calixarene epoxy resin (Resin B) by theindirect method is described in Example A and a further "lower rim"calixarene epoxy resin (Resin A) was made by the method described in DD278139A1. These examples are included for comparison and illustrate themuch greater ease of preparation and better properties of the "upperrim" calixarene epoxy resins of this invention.

Example A--Epoxy resin fromOcta-t-butyl-octahydroxycalix[8]axene(p-t-butylcalix[8]arene) (Resin B)

The method used to make p-t-butylcalix[8]arene starting material wasbased on that of Gutsthe et a.l, 1981, J. Am. Chem. Soc, 103, 3782. Anepoxy. resin is difficult to synthesize by direct reaction withepichlorohydrin on this type of "lower rim" calixarene (see FIG. 1 ) andyields only the chlorohydrin derivative using the procedures describedabove. Thus the ether: Octa-t-butyl-octaalloxycalix[8]arene was preparedfirst.

The p-t-butylcalix[8]arene (1.07 g, 0.00083 mole) was dissolved in dry.DMF (25 ml) and placed in an apparatus purged with argon. After thetemperature of the solution had been raised to 60° C., sodium hydride(1.3 g, 0.054 mole) freshly washed with dried benzene was added inportions and then the mixture was held at this temperature for 1 h.Allyl bromide (10 ml, 0.116 mole) was added dropwise to the stirredreaction mix and the temperature increased to 110° C. during theaddition. When the temperature had dropped back to 90° C. aftercompletion of the addition the reaction mix was brought to 120° C. andkept at this temperature for 2 h. After cooling the reaction mixture wasdiluted with water (50 ml) and the product extracted with ether (2×50ml). The combined etherial extracts were washed with dilute brine (50ml), dried with Na.sub. SO₄ and evaporated to dryness.

The crude residue was recrystallized from CHCl₃ /MeOH and thentoluene/heptane to give colourless crystals of the octa allyl ether(0.61 g, 46%) mp 226°-229° C. Found: C, 82.6; H, 9.3. (C₁₄ H₁₈ O)₈requires C, 83.1; H, 9.0%. ¹ H n.m.r. (CDCl₃) δ: 1.11, s, (CH₃)₃ C ;4.02, m, 32H, CH₂ and OCH₂ ; 4.84, m, 4.94, m, 5.12, m, 16H. =CH₂ 5.74,m, 8H, --CH =; 7.00, s, 16H, aromatic.

Epoxidation of the allyl ether

The allyl ether (1.616 g, 0.001 mole) in dichloromethane (10 ml) wasmixed with a solution of m-chloroperbenzoic acid (1.38 g, 0.008 mole) indichloromethane (10ml) and stirred at room temperature for 24 h. At theend of this time the precipitated m-chlorobenzoic acid was filtered off(usually less recovered than the theoretical amount) and the filtratewas passed through a short column packed with neutral alumina in orderto remove the rest of the acid and peroxides. Fractions were collected,checked for absence of peroxides and evaporated. A total of 1.090 g ofmaterial was recovered from the column in two main fractions. ¹ H nmr.indicated the presence of epoxy groups in both fractions. This resin hadan epoxy equivalent weight of 499 g.

Example--Preparation of the epoxy resin fromC-Methylcalix[4]resorcinarene

Method A

C-Methylcalix14]resorcinarene (50 g, 0.0919 mole) which was prepared bythe method of Cram et al, 1988, J. Am. Chem. Soc, 110, 2229 was added toa mixture of epichlorohydrin (340 g, 288 ml, 3.7 mole), 2-propanol (288ml) and methanol (96 ml) and stirred. After a short time a solution wasobtained and the temperature was raised to 50° C. in an oil bath. Tothis solution was added dropwise a solution of NaOH (29.4 g, 0.735 mole)in methanol (2130 ml). The addition took about 1 h and the temperaturewas kept at 50° C. The reaction mixture was stirred for a further 4 h at50° C. after the addition. On cooling, the inorganic salts were filteredoff and then the filtrate was evaporated leaving a residue which wasthen redissolved in dichloromethane (100 ml). Insoluble matter wasfiltered off and the filtrate was treated with dilute brine (100 ml) andthe pH adjusted to 5 with a little acetic acid. The emulsion so formedwas broken by filtration through celite. After a further wash withwater, the organic layer was dried over sodium sulphate and filtered.Coloured impurities were removed by passing this solution through ashort (42×75 mm) column of neutral alumina. The eluate was evaporated togive the resin as a brown friable powder,(82 g), m.p.148°-154° C. ^(i) Hn.m.r. (CDCl₃) δ: 1.48, m; 2.74, m; 3.30, m; 3.6, sharp peaks; 3.87, m;4.61, m; 6.33, m; 7.20, m. The n.m.r. exhibits great complexityindicating a whole family of partially epoxidized materials. This resinhad an epoxy equivalent weight of 175 g which agrees with the ¹ H n.m.r.integral data in suggesting an average of 4 epoxy groups per molecule.

Method B

C-Methylcalix[4]resorcinarene (75 g, 0.138 mole) was prepared asdescribed in Method A above was weighed into a reaction flask and thenepichlorohydrin (216 ml, 2.76 mole), 2-propanol (45 ml), methanol (21ml) and finally N,N-dimethylbenzylamine (0.375 ml) were added, blanketedwith argon and stirred mechanically. A solution was obtained quickly andthe temperature was raised to 50° C. in an oil bath and maintained atthis temperature with stirring for 1 h. Then a solution of NaOH (44.2 g,1.104 mole) in water (270 ml) was added dropwise over about 1 h whilstthe temperature was kept near 50° C. Stirring was continued for afurther 3 h at 50° C. and then overnight at room temperature.

Next day the pH of the mixture was adjusted to approximately 5 by theaddition of glacial acetic acid in about 50% of the runs done, twophases separated in the reaction flask allowing easy separation of theupper aqueous phase and simplification of the subsequent evaporation).The organic phase was then evaporated to dryness. If on the other handtwo phases failed to separate the whole reaction mixture was evaporatedto dryness. The solid residue was extracted with dichloromethane (400ml) by mechanical stirring (the epoxy resin is very soluble indichloromethane) and was filtered off on a large Buchner funnel having alayer of celite to aid the rather difficult filtration. The residue wasre-extracted with further dichloromethane (200 ml) and the combineddichloromethane extracts were washed once with water (200 ml), driedwith Na₂ SO₄ and evaporated to dryness. The residue is once againdissolved in dichloromethane (300 ml) and filtered once again throughcelite to obtain a clear solution. Evaporation to dryness yielded theepoxy resin as a friable light buff powder (84.7 g) of epoxy equivalentweight 195 g and mp 172°-192° C.

Example 2--Preparation of epoxy resin from C-ethylcalix[4]resorcinarene

C-Ethylcalix[4]resorcinarene prepared by the established procedure wastreated with epichlorohydrin as described in Example 1 above to give aresin as a friable solid with an epoxy equivalent weight of 238 g.

Example 3--Epoxy resin from C-isopropylcalix[4]resorcinarene

The starting C-isopropylcalix[4]resorcinarene prepared by a variation ofthe established procedure was treated as in Example 1 above withepichlorohydrin to give a resin softening at 120°-125° C. and with anepoxy equivalent weight of 247 g. ¹ H n.m.r. (CDCl₃) was complex: 0.85,m, 20-24H; 1.5, m, 4H; 2.73, m. approx. 12H; complex region 3-4.6;6.35,m, approx. 3H; 7.2, m, approx 2H.

Example 4--Epoxy resin from C-phenylcalix-[4]resorcinarene

Resorcinol (80.2 g, 0.29 mole) and benzaldehyde (74 ml, 0.729 mole) in amixture of 95% ethanol (580 ml) and concentrated HCl (146 ml) wasstirred mechanically at 80° C. for 11 days under argon. At the end ofthis time the yellow precipitate was filtered and washed by suspendingin 95% ethanol stirring for 30 min and then filtering; this washingprocedure was repeated twice. The crude product was dissolved in 2MNaOH, filtered and then acidified with acetic acid whereupon aprecipitate formed. Filtration and drying yielded the product as a brownsolid, 134 g (93%). ¹ H n.m.r. (NaOD) δ: 5.62, m, 4H; 5.98, s, 4H, CH;6.26, m, 4H; 7.14, m, 20-24H.

Preparation of the epoxy resin followed essentially the same procedureas above except that the calixarene was suspended in the reactionmixture of epichlorohydrin and alcohol. The starting material went intosolution as the reaction proceeded. On work up and chromatography onalumina the resin was obtained as a dark friable solid, of epoxyequivalent weight, 186 g.

Example 5--Epoxy resins from partially methylated C-methylcalix[4]resorcinarene

C-Methylcalix[4]resorcinarene (10 g, 0.018 mole) in a mixture ofanhydrous K₂ CO₃ (10.2 g) and dry acetone (200 ml) was treated withiodomethane (15.7 g. 0.11 mole) and stirred under argon at reflux for 16h. After [filtering off the sails, the acetone solution was evaporatedto dryness and partitioned between dichloromethane and dilute brine atpH 3. Further extractions with fresh dichloromethane were carried outand the combined dichloromethane layers, were washed once with brine,dried (Na₂ SO₄) and evaporated to dryness (10.6 g). This residue wasredissolved in dichioromethane, passed through a short column ofFlorisil (Registered Trade Mark) and the eluate evaporated to give themixed methyl ethers, 8.1 g as an oil. HPLC showed this product to be amixture of components but ¹ H nmr. was consistent with methylation.There was always present in these mixtures some of the octamethyl etherof C-methylcalix[4]resorcinarene, an authentic sample of which had beenprepared and characterized fully.

Products of varying methoxy content were obtained by varying the amountof iodomethane used. The preparation of epoxy resins from these oilsfollowed the procedures described above. By this means epoxy resinshaving epoxy equivalent weights of 241, 313, 335 and 403 g wereprepared.

Example 6 Epoxy resin from C-propyl-calix[4]resorcinarene

Epoxy, resin from C-propylcalix[4]resorcinarene was made as for example1 using the appropriate starting calixarene. The resin had m.p. 115°-130° C. and an epoxy equivalent weight of 215 g.

Example 7--Epoxy resin of C-methyl-2-methylcalix[4]resorcinarene

Epoxidation of the C-methyl-2-methylcalix[4]resorcinarene by theprocedures already described gave an epoxy resin of epoxy equivalentweight, 221 g.

Example 8--Epoxy resin of mixed isomers-of C-methylcalix[4]resorcinarene

(a) Starting calixarene A stirred mixture of resorcinol (11.01 g, 0.1mole) and acetaldehyde (4.41 g, 0.1 mole) in water (40 ml) was acidifiedby careful addition of concentrated HCl (10 ml). There was an exothermicreaction and a precipitate formed rapidly. Stirring was continued for 1h at 75° C. and then the mixture was cooled and the precipitatedcalixarene filtered off, washed with water and dried, (14 g). Thisproduct contains about 25% (h.p.l.c.) of the cis,trans,cis isomer and75% of the "normal" all cis isomer described above.

(b) Epoxidation. Using the procedure above yielded an epoxy resin of themixed isomers having m.p.118°-128° C. and an epoxy equivalent weight of180 g.

Example 9

(a) Preparation of a typical curable formulation

The resin prepared in Example 1 (3.63 g) was added in portions withstirring to Epikote 8283 IQ (Registered Trade Mark) a commercial DGEBAtype epoxy resin (4.01 g) at 127° C. The amine hardener, p-aminophenylsulphone (DDS) (2.36 g) was added in portions to the resulting oil withstirring. Additives, for example CTBN rubbers to make toughenedformulations if desired were added at this stage. This mixture was thendegassed by evacuation (1 mm Hg) for 8 min and BF₃ -ethylamine catalyst(Anchor 1948 (Registered Trade Mark)) was added in one lot withstirring. The mixture was degassed for a further 4 min under the sameconditions as before.

(b) Curing and properties of a typical formulated resin

After pouring into appropriate moulds curing was accomplished by heatingat 100° C. for 1 h, 140° C. for 1 h, and then 180° C. for 4 h. This neatcured resin had a T_(g) (Tan δ max) of 281° C. and a modulus of 2.1 GPa.Neat resin fracture toughness as measured by the compact tension testwas 0.40 MPa.m^(1/2). The properties of other formulations of the resinof Example 1 are given in Table 2.

Example 10--Other Curable Formulations

The method of Example 9(a) was used to formulate resins prepared as inExamples 1-8. These formulated resins when cured as in Example 9(b) givethe fracture toughness values shown in Table 2.

Example 11--Preparation of a typical prepreg

Method (a). The resin formulation (55 g) prepared as described inExample 9 (a) was dissolved in purified methyl ethyl ketone (55ml) andpainted onto Fiberite (Registered Trade Mark) High PerformanceStructural W322 woven carbon fibre cloth. The prepreg was dried in astream of warm air for 2 h and then "B" staged in an oven at 90° C. for100 sec. This prepreg had a mean resin content of 43% and had good drapeand slight tack. The temperature and time of "staging" was varied tosuit the requirements of each formulation.

Method (b). With some formulations it was more advantageous to dissolveepoxy resin, hardener and any additives in dichloromethane, and producethe prepreg from this solution.

These prepregging solutions were also suited to machine prepregging ofcloth or uni-directional tape.

Example 12--Fabrication into sample composite laminates

A 20 ply laminate was laid up from pre-preg made as in Example 9according to BSS 7273 and cured in an autoclave under a pressure of 620kPa using the curing schedule described above. The cured laminate had adensity of 1.56 g/cm³, a fibre volume of 57% and a fibre weight onweight of composite of 62.8%.

2 ply, 12 ply, and 5 ply laminates were also made from the prepreg asdescribed above and cured in an autoclave or on a hot platten press.

Example 13--Impact characteristics

2 Ply laminates when tested on an ICI Impact tester had an average loadat break of 166.1 Newtons and average energy at break of 355 Joules.

Example 14--Mode I Fracture Toughness of typical Laminates

20 Ply cloth composite laminates were prepared from pre-pregs and testedaccording to BSS 7273. Values for some formulations are shown in Table4.

Example 15--Laminate Static Tensile Properties

12 Ply laminates of prepregs made from various formulations of the newresins were prepared and tested according to BMS 8-256F for Tensileproperties. Results are shown in Table 5.

Example 16--Toughening of Resins with Rubbers

Admixture of CTBN rubber (Hycar 1300x13 (Registered Trade Mark), 10p.h.r.) to a curable formulation prepared as in Example 9(a) above,followed by curing as a neat resin sample as in Example 9(b) orprepregging the formulation and then preparation of a laminate as inExamples 11 and 12. yielded samples that were significantly tougher thanuntreated samples (Tables 2 and 6).

                  TABLE 2                                                         ______________________________________                                        Properties of Cured Formulated Resins                                                                              Fracture                                                  Mode of      Additive                                                                             Toughness                                Resin   Tg       toughening   %      Kq*                                      ______________________________________                                        Example 1                                                                             281      none         none   0.40                                     Example 1                                                                             282      CTBN 1300 × 8                                                                         5     0.46                                     Example 1                                                                             284      CTBN 1300 × 8                                                                        10     0.57                                     Example 1                                                                             277      CTBN 1300 × 8                                                                        15     0.51                                     Example 1                                                                             290, 235 CTBN 1300 × 8                                                                        20     0.53                                     Example 1                                                                             285      CTBN 1300 × 13                                                                       10     0.68                                     Example 1                                                                             288      CTBN 1300 × 13                                                                       15     0.58                                     Example 1                                                                             293      ULTEM        10     0.65                                     Example 2                                                                             277      none         none   0.56                                     Example 3                                                                             271      none         none   0.44                                             (225)                                                                 Example 4        none         none   0.49                                     Example 5                                                                             210      Methylation  none   0.81                                     (EQW 313)                                                                     Example 5                                                                             216      Methylation  none   0.53                                     (EQW 241)                                                                     Example 6        none         none   0.44                                     Example 7                                                                             282      none         none   0.50                                             (212)                                                                 Example 8        none         none   0.57                                     Resin A 199      none         none   0.52                                     ______________________________________                                         Notes:                                                                        All resins were cured under the a same conditions with BF.sub.3ethylamine     catalyst present (0.33 phr).                                                  *Fracture toughness based on multiple values, in the units Mpa.m.sup.1/2 

                  TABLE 3                                                         ______________________________________                                        Comparison of Tg values (DMTA) obtained for some of                           the cured neat calixarene epoxy resin formulations                            and some other glycidyl ether resin formulations                              Resin System     Tg (Tan δ) °C.                                                               Description                                      ______________________________________                                        DGEBA            211                                                          Xanthene.sup.1   242                                                          Example 1        281                                                          Example 2        277                                                          Example 3        271 (225)   D.sup.2                                          Example 5 (EQW.sup.3 313)                                                                      210                                                          Example 7        282 (212)   D.sup.2                                          Resin A          199         B.sup.4                                          ______________________________________                                         Notes:                                                                        .sup.1 Experimental resin of Diglycidyl ether type                            .sup.2 Shoulder on lower temperature side of Tan δ curve                .sup.3 Epoxy Equivalent weight                                                .sup.4 Broad Tan δ peak                                            

                  TABLE 4                                                         ______________________________________                                        Mode I Fracture Toughness Values for some Typical Laminates                            Fracture Toughness J/m.sup.2                                         Formulation                                                                              Initiation    arrest  area                                         ______________________________________                                        1 (Resin   370           232     288                                          Example 1)                                                                    2 (Resin   321           237     267                                          Example 2                                                                     3 (Resin   327           197     257                                          Example 1)                                                                    5 (Resin   380           246     305                                          Example 6)                                                                    ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Some Static Tensile properties of Typical Laminates                                                             Ultimate                                            Ultimate Tensile                                                                           Modulus of   Tensile                                     Formulation                                                                           Strength MPa Elasticity (GPa)                                                                           Strain (%)                                  ______________________________________                                        1 (Resin                                                                              585          61.2         0.957                                       Example 1                                                                     2 (Resin                                                                              561          58.2         0.965                                       Example 2)                                                                    4 (Resin                                                                              596          58.7         1.017                                       Example 1)                                                                    ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Effect of added CTBN Rubber on the Mode I Fracture                            Toughness Values of Laminates containing Resin from                           Example 1                                                                                Fracture Toughness J/m.sup.2                                       Formulation  Initiation   arrest  area                                        ______________________________________                                        1 (Resin     370          232     288                                         Example 1) no                                                                 rubber                                                                        4 (Resin     477          279     364                                         Example 1), 10                                                                p.h.r. of CTBN                                                                rubber                                                                        ______________________________________                                    

We claim:
 1. A macrocyclic compound of the formula (I) ##STR4## whereinn is an integer from 3 to 10;R¹ and R³ are either the same or differentand are hydrogen, hydroxyl, alkoxy, allyloxy, or epoxypropyloxy; R² ishydrogen, aralkyl optionally substituted with halogen, alkyl optionallysubstituted with halogen, or aryl optionally substituted with halogen;R⁴ is hydrogen, alkyl optionally substituted with halogen, aralkyloptionally substituted with halogen, or aryl optionally substituted withalkyl and/or halogen; R⁵ is hydrogen, aryl or alkyl;with the provisothat the compound contains on average at least one epoxy group permolecule.
 2. A compound as claimed in claim 1, characterized in thateach of R¹ and R³ is hydroxyl, alkoxy or epoxypropyloxy, R² is hydrogen,R⁴ is methyl, ethyl or propyl and R⁵ is hydrogen.
 3. A compound asclaimed in claim 2, characterized in that the number of hydroxyl (orhydroxyl+alkoxy) groups present is approximately equal to the number ofepoxypropyloxy groups.
 4. A method for the preparation of a macrocycliccompound of the formula (I) as claimed in claim 1, characterized in thatsaid method comprises epoxidizing a compound of the formula ##STR5##wherein n, R², R⁵ and R⁴ are as defined for the compound of formula (I)in claim 1 and R⁶ and R⁷ are either the same or different and areselected from hydrogen or a masking group, with the proviso that atleast one of R⁶ and R⁷ is hydrogen.
 5. A method as claimed in claim 4,characterized in that the epoxidation is performed usingepichlorohydrin.
 6. A curable epoxy resin formulation, characterized inthat the resin formulation comprises at least macrocyclic compound ofthe formula (I) as defined in claim 1, together with other epoxy resinsand/or additives selected from the group consisting of tougheningpolymers, hardeners, reinforcements, fillers and catalysts.
 7. A curableepoxy resin formulation as claimed in claim 6, characterized in that theother epoxy resin is a diglycidyl ether of bisphenol A (DGEBA) and theadditive is 4,4'-diaminodiphenylsulphone or BF₃ -ethylamine.
 8. Animpregnated fibre reinforced material, characterized in that the fibrereinforcements are impregnated with an epoxy resin formulation asclaimed in claim
 6. 9. An advanced composite material comprising afibrous material in a matrix of a cured epoxy resin, characterized inthat the cured epoxy resin is formed from an epoxy resin formulation asclaimed in claim
 6. 10. A method as claimed in claim 4 wherein themasking group is an alkyl group.